I. Field
The following description relates generally to wireless communications, and more particularly to transmission of static context and semi-static context during handover of mobile device to another cell.
II. Background
Wireless communication systems are widely deployed to provide various types of communication; for instance, voice and/or data can be provided via such wireless communication systems. A typical wireless communication system, or network, can provide multiple users access to one or more shared resources (e.g., bandwidth, transmit power, . . . ). For instance, a system can use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), Third Generation Partnership Project (3GPP) Long-Term Evolution (LTE) systems, Orthogonal Frequency Division Multiplexing (OFDM), and others.
Generally, wireless multiple-access communication systems can simultaneously support communication for multiple mobile devices. Each mobile device can communicate with one or more base stations via transmissions on forward and reverse links. The forward link (or downlink) refers to the communication link from base stations to mobile devices, and the reverse link (or uplink) refers to the communication link from mobile devices to base stations. This communication link can be established via a single-in-single-out, multiple-in-signal-out, or a multiple-in-multiple-out (MIMO) system.
For instance, a MIMO system can employ multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas can be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels can correspond to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system can support a time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions can be on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This can enable the access point to extract transmit beamforming gain on the forward link when multiple antennas are available at the access point
Wireless communication systems oftentimes employ one or more base stations that provide a coverage area. A typical base station can transmit multiple data streams for broadcast, multicast and/or unicast services, wherein a data stream may be a stream of data that can be of independent reception interest to a mobile device. A mobile device within the coverage area of such base station can be employed to receive one, more than one, or all the data streams carried by the composite stream. Likewise, a mobile device can transmit data to the base station or another mobile device.
Typically, information (e.g., data, header information, etc.) associated with a mobile device can be compressed before being transmitted to facilitate efficient communication in a wireless communication environment. For instance, a Robust Header Compression (RoHC) engine can be employed to compress information, such as headers (e.g., Internet Protocol (IP) header, Uniform Datagram Protocol (UDP) header, Real-Time Transfer Protocol (RTP) header, communicated between a base station and a mobile device. Conventionally, in certain communication systems (e.g., 1x, Data Optimizer (DO), (HSPA)), the RoHC function resides in the Base Station Controller (BSC) or Radio Network Controller (RNC), and RoHC context re-establishment is required only for inter-BSC handovers or inter-RNC handovers, which typically occur far less frequently than intra-BSC handovers or intra-RNC handovers.
However, in communication systems, such as Long Term Evolution (LTE) communication systems, the Packet Data Convergence Protocol (PDCP) function typically resides in the base station (e.g., eNode B) and not in an access gateway. As a result, the RoHC context has to be re-established at each inter-base station handover of the mobile device from one base station to another base station. This can result in larger packets of data, such as IP header, RTP header, and UDP header, being transmitted in an uncompressed form to the mobile device until RoHC context is re-established, where after the RoHC context is re-established data can be transmitted between the mobile device and base station in a more desirable compressed form. Re-establishing RoHC context at each handover can result in a significant capacity loss and/or latency increase for some applications, such as voice over IP (VoIP) and mobile network gaming, which can result in a quality or user-experience degradation at handover events.
Certain information, such as the portions of the IP header (e.g., version, flow label next header, source address, destination address, etc.), RTP header (e.g., version extension, synchronization source (SSRC), etc.), and UDP header (e.g., source port, destination port), is static context or semi-static context that can be the same or virtually the same, or changed relatively infrequently, for a flow. When a handover of a mobile device from one base station to a disparate base station occurs, there is typically a short period of time between the time that the message to the mobile device directing the handover is sent to the mobile device and the time when the handover occurs. As it is desirable to establish RoHC context to facilitate compressing data for transmission, it is desirable to be able to at least partially or fully re-establish RoHC context during a handover in an efficient manner.